1. Field of the Invention
The present invention relates to a limit control switch, and more particularly to a limit switch control device.
2. Description of the Prior Art
Common limit switch control devices mainly comprise the following two types:
As shown in FIG. 7, one type of the common limit switch control device is provided with a moving space 10 where a mover 11 is arranged. The mover 11 is combined on a shaft 12 which is driven by a drive element 13. The moving space 10 is interiorly provided a lower limit switch 14 at one end thereof and an upper limit switch 15 at the other end thereof. The lower limit switch 14 and the upper limit switch 15 are directly connected to the drive element 13. When the drive element 13 drives the shaft 12 to move, the mover 11 can be synchronously moved. After the mover 11 which is moving forwards contacts the upper limit switch 15, the upper limit switch 15 will stop the drive element 13 from driving the mover 11 to move forwards while allowing the mover 11 to move backwards. Otherwise, after the mover 11 which is moving backwards contacts the lower limit switch 14, the lower limit switch 14 will stop the drive element 13 from driving the mover 11 to move backwards while allowing the mover 11 to move forwards. However, this limit switch control device has the following disadvantages:
1. Poor practicality: due to the manner in which the lower limit switch 14 and the upper limit switch 15 are arranged in the moving space 10, the positions where the lower limit switch 14 and the upper limit switch 15 cannot be changed. Therefore, the travel distance of the mover 11 cannot be adjusted as desired;
2. High structure damage rate: the electric current directly flows through the lower limit switch 14 and the upper limit switch 15, so it is likely to cause damage to the contacts of the lower limit switch 14 and the upper limit switch 15, thus causing high structure damage rate;
3. Short service life: because the mover 11 directly contacts the lower limit switch 14 and the upper limit switch 15, after a long time of use, it is possible to cause the structural damage to the lower limit switch 14 and the upper limit switch 15, thus shortening the structure service life.
As shown in FIG. 8, the other type of the common limit switch control device is provided with a sensor 22 combined on a shaft 21 in a combining tube 20. The shaft 21 is driven by a drive element 23, and the sensor 22 moves with the shaft 21. A lower limit reed switch 24 and an upper limit reed switch 25 are mounted on the combining tube 20. The two limit reed switches 24, 25 can be controlled to move on the combining tube 20, so as to be selectively fixed at any two positions. This limit switch control device is further used together with a control unit 30 including a drive element control circuit 31 and a limit switch control circuit 32. The drive element control circuit 31 is connected to the drive element 23, and the limit switch control circuit 32 is connected to the two limit reed switches 24, 25.
When the drive element 23 drives the shaft 21 to move in the combining tube 20, the sensor 22 is synchronously moved with the shaft 21. Upon reaching the position where the upper limit reed switch 25 is located, the sensor 22 will send the corresponding signal to the drive element control circuit 31 though the limit switch control circuit 32. After that, the drive element control circuit 31 will make the drive element 23 stop driving the shaft to move forward but enable it to have the ability of controlling the shaft 21 to move backwards, otherwise, on the analogy of this. The travel distance of the shaft 21 can be adjusted by moving the lower limit reed switch 24 and the upper limit reed switch 25 on the combining tube 20. However, this limit switch control device has the following disadvantages:
1. Complex installation: the lower limit reed switch 24 and the upper limit reed switch 25 are exteriorly connected to the control unit 30, and the drive element is also exteriorly connected to the control unit 30, so that a lot of wires are required for installation, thus increasing the installation complexity;
2. High cost: the drive element 23 and the shaft 21are controlled by the lower limit reed switch 24 and the upper limit reed switch 25 through the external control unit 30, which is an additional installation having the disadvantage of high cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.